Cambridge A Level Chemistry 9701 — 2008 May/June Paper 5 · Variant 1

This document consists of 11 printed pages and 1 blank page. SPA (DR/DR) T60103/4 © UCLES 2008 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You are advised to show all working in calculations. Use of Data Booklet is unnecessary. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. CHEMISTRY 9701/05 Paper 5 Planning, analysis and evaluation May/June 2008 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 2 Total * 4 5 3 3 2 8 7 5 0 0 *

2 9701/05/M/J/08 For Examiner’s Use © UCLES 2008 1 The equations for the complete combustion of the first five members of the alcohol homologous series are shown below. methanol CH3OH(l) + 1½O2(g) CO2(g) + 2H2O(l) ethanol CH3CH2OH(l) + 3O2(g) 2CO2(g) + 3H2O(l) propan-1-ol CH3CH2CH2OH(l) + 4½O2(g) 3CO2(g) + 4H2O(l) butan-1-ol CH3CH2CH2CH2OH(l) + 6O2(g) 4CO2(g) + 5H2O(l) pentan-1-ol CH3CH2CH2CH2CH2OH(l) + 7½O2(g) 5CO2(g) + 6H2O(l) You are to plan an experiment to determine the enthalpy change of combustion under laboratory conditions, ΔHc, for each of the five alcohols using the apparatus and information below. thermometer water copper can spirit lamp containing selected alcohol [4.2 J of heat energy raise the temperature of 1 cm3 (1 g) of water by 1 °C.] (a) Inspection of the products of the five equations shows that from ethanol to pentan-1-ol each equation has one more mole of CO2 and one more mole of H2O produced per mole of alcohol than the equation above it. What difference between the structures of adjacent alcohols is responsible for these additional combustion products? …[1]

3 9701/05/M/J/08 [Turn over For Examiner’s Use © UCLES 2008 (b) There is a trend in ΔHc for these five alcohols. Use your answer to (a) to sketch the trend indicated by the equations. 1 2 3 4 5 number of carbon atoms in the alcohol
Hc [1] (c) Identify each of the following variables in the experiment to determine the enthalpy change of combustion of an alcohol using the apparatus in the diagram. The independent variable is ……………………………………………………….. The dependent variable is ………………………………………………………… Two variables to be controlled in this experiment are 1 … 2 … [3]

4 9701/05/M/J/08 For Examiner’s Use © UCLES 2008 (d) You are to plan a step-by-step method to determine the enthalpy change of combustion, ΔHc, for each of the alcohols in turn. You should use the apparatus shown in the diagram on page 2 and any other apparatus required that is normally found in a school or college laboratory. You need only explain how the method will be used for ethanol. Your method should cover the following points. • the precision of the apparatus to be used • the way in which the independent variable is varied between experiments • measurement of the dependent variable • appropriate quantities to be used • the raw data to be collected • how this data is to be processed for ethanol [4.2 J of heat energy raise the temperature of 1 cm3 (1 g) of water by 1 °C.] Method … … … … … … … … … … … … … … … … … … …

5 9701/05/M/J/08 [Turn over For Examiner’s Use © UCLES 2008 … … … … … … … … … Processing of raw data [Mr: CH3CH2OH, 46] … … … … … … [6] (e) Prepare a single table to show, for each alcohol, all of the measurements obtained directly from the experiment and the information processed from these data. Your table should show the correct units for each of the headed columns. [2]

6 9701/05/M/J/08 For Examiner’s Use © UCLES 2008 (f) The apparatus shown in the diagram on page 2 and used in the experiment you have described is inefficient as much of the energy released from the burning alcohol is lost to the atmosphere. You are to plan two simple changes to the apparatus shown on page 2 that will reduce the loss of heat energy to the atmosphere. Draw a diagram of your improved apparatus, indicating and explaining how these changes will reduce the loss of heat energy. improvement 1 … … … … … … improvement 2 … … … … … … [2] [Total: 15]

7 9701/05/M/J/08 [Turn over For Examiner’s Use © UCLES 2008 2 Basic copper(II) carbonate is a mixture of copper(II) carbonate and copper(II) hydroxide with varying amounts of water of crystallisation. The formula may be represented as CuCO3.Cu(OH)2.xH2O. A group of students conduct an experiment to determine the relative formula mass and the actual value of x in the formula of the basic copper(II) carbonate, CuCO3.Cu(OH)2.x H2O. This basic carbonate decomposes on heating. CuCO3.Cu(OH)2.x H2O(s) 2CuO(s) + CO2(g) + (x+1)H2O(g) Each student is provided with a sample of the solid basic carbonate and the following apparatus. • a boiling-tube • a test-tube holder • a chemical balance, reading to 2 decimal places • a Bunsen burner Method • The empty boiling-tube is weighed. • The sample of basic copper(II) carbonate is tipped into the boiling-tube which is reweighed. • The carbonate is heated, gently at first, as carbon dioxide and water vapour are given off. The carbonate is then heated strongly. • Heating is continued until all of the green colour of the initial solid has turned to the black colour of copper(II) oxide. • The apparatus is cooled and the mass of the tube and residue is measured.

8 9701/05/M/J/08 For Examiner’s Use © UCLES 2008 The results of the experiment are recorded below. A B C D E F student mass of empty boiling-tube /g mass of boiling-tube and basic carbonate before heating /g mass of boiling-tube and residue after heating /g 1 10.32 11.19 10.92 2 10.05 11.56 11.09 3 10.11 12.33 11.24 4 9.94 12.39 11.62 5 9.99 13.73 12.56 6 10.23 14.68 13.28 7 10.01 15.19 13.56 8 9.87 15.80 13.97 9 9.96 16.62 14.66 10 9.84 17.83 15.46 (a) Use the additional columns of the table to record the calculated values that will enable you to determine the relative formula mass, Mr , of basic copper(II) carbonate and the value of x in CuCO3.Cu(OH)2.xH2O. You may use some or all of the columns. Label the columns you use, including the units and an equation to show how the value is calculated. You may use the column headings A to F in the equations e.g. C – B. Make certain that your processed values show the precision of the apparatus used. [2]

9 9701/05/M/J/08 [Turn over For Examiner’s Use © UCLES 2008 (b) Present the values calculated in (a) in graphical form. Draw the line of best-fit. [4]

10 9701/05/M/J/08 For Examiner’s Use © UCLES 2008 (c) Give the co-ordinates of the most significant anomalous point. By reference to the instructions for the experiment suggest an explanation for this anomaly. co-ordinates … explanation … … …[2] (d) The students note that points plotted when using higher masses of the basic carbonate lie to one side of the line of best-fit. Suggest an explanation for this observation. … … …[1] (e) How would you modify the experiment to overcome the problem described in (d)? … … …[1] (f) Draw construction lines on the graph to derive values to enable you to calculate the relative formula mass of the basic copper(II) carbonate and the value of x in CuCO3.Cu(OH)2.xH2O. Values read from graph, including units x-axis … y-axis … Calculation of the relative formula mass, Mr [Ar: H, 1.0; C, 12.0; O, 16.0; Cu, 63.5]

11 9701/05/M/J/08 For Examiner’s Use © UCLES 2008 (f) continued Calculation of x in the formula [2] (g) By considering the data you have processed and the graph you have drawn, explain if the experimental procedure described is suitable for the determination of the relative formula mass of the basic carbonate. … … … … …[1] (h) What other measurements could be made during the course of the experiment to provide alternative data to determine the relative formula mass and the value of x ? … … … …[1] (i) Explain why the precision of the experiment would improve if students used a chemical balance weighing to 3 decimal places. … … … …[1] [Total: 15]

12 9701/05/M/J/08 BLANK PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2008 question paper 9701 CHEMISTRY 9701/05 Paper 5 (Planning, Analysis and Evaluation), maximum raw mark 30 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the report on the examination. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the May/June 2008 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 Breakdown of marks Question 1 Question 2 Skill Total marks Statement Marks Defining the problem P 5 5 0 Planning 15 marks Methods M 10 10 0 Dealing with data D 8 0 8 Evaluation E 4 0 4 Analysis, conclusions and evaluation 15 marks Conclusion C 3 0 3 Question Sections Statement Indicative material Mark 1 (a) PLAN Problem P3 CH2 identified as structural unit or different number of carbon and hydrogen atoms 1 1 (b) PLAN Problem P3 Accept only (a straight line / points in a straight line / bars in a straight line) showing increasing numerical value from C1 to C5. Freehand sketches are acceptable 1 1 (c) PLAN Problem P1 Independent (Controlled) variable (i) mass/moles of alcohol identified as independent variable. (do not accept amount) (ii) temperature rise or change identified as independent variable. (iii) (alcohol chosen / number of carbon atoms in alcohol / carbon chain length) identified as independent variable or duration of experiment identified as independent variable 1 P2 Dependent variable (consequential to the Independent variable) (i) (temperature rise or change / heat produced / energy change) identified as dependent variable. (ii) Ignore any reference to ∆Hc (iii) mass/moles of alcohol identified as dependent variable. (do not accept amount) (iv) (temperature rise or change or final temperature / heat produced / energy change) identified as dependent variable or mass/moles of alcohol identified as dependent variable. Ignore any reference to ∆Hc 1

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 Question Sections Statement Indicative material Mark 1 (c) contd. PLAN Problem P4 Two variables to be controlled selected from: (i) mass or volume of water, (allow amount here) (ii) initial temperature of water or ambient/room temperature (iii) use of same metal can or same position of the burner If alcohol chosen/chain length is chosen as independent variable (iv) mass/moles is controlled 1 1 (d) Part 1 PLAN Methods M6 M1 M2 M6 M5 M5 1 Uses thermometer capable of reading to 1 °C or better or balance capable of reading to 0.1 g or better. 2 Burns stated or measured mass or moles of ethanol completely, or burns ethanol to get a particular temperature rise, or burns ethanol for a particular length of time. 3 Measures initial and final temperature, or measures initial and final masses of ethanol. 4 Shows how the mass of ethanol is converted to moles. (Items 3 & 4 can be taken from the table or the calculation.) (46 must be shown in an expression – not the symbol Mr) 5 Uses mc∆T to calculate heat absorbed by the water in the can. We need to look for either suggested numbers or algebraic symbols (not just mc∆T. Accept ∆T but not theta unless defined. 6 Scales heat absorbed for 1 mol of ethanol (correct units are needed here) 1 1 1 1 1 1 1 (e) PLAN Methods M9 M9 Draws up table(s), for range of alcohols, to show the following headings (with correct units, there is no penalty here for representing the units incorrectly but EACH COLUMN in the table needs to have correct units recorded (even if this means several columns with the same unit). Allow K for °C): (i) two weighings + mass of alcohols or two temperature readings + ∆T (ii) The “other” measured quantity: mass of alcohol used or ∆T. If the table is for less than all the alcohols apply a penalty of 1 mark Safety mark: If the table only contains the following recordings; initial and final mass and initial and final temperature, give one mark On pages 4 & 5 penalise a unit error only once. 1 1

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 1 (f) PLAN Methods M5 M5 One improvement to reduce heat loss given in diagram and by explanation. From: (i) insulation on sides but not bottom of can (ii) lid on can (iii) draught shield fitted (iv) lower tripod or raise burner (v) replacement of tripod with insulated support Each suggestion should be supported by an appropriate reason and for such items as ‘move the flame closer to the can’ we need to know how this is to be done. Heat lost to the surroundings or atmosphere etc., generates no mark. Heat loss could be through the top of the cup (convection) or through the sides of the can (conduction) Second improvement from same list Give one of these two marks for two listed improvements without explanation. 1 1 Qn 1 Total 15

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 Question Sections Statement Indicative material Mark 2 (a) ACE Data D1 D2 Labels all additional columns used, including units (e.g. /g or (g)) and an appropriate equation: the mass of basic copper(II) carbonate (B–A) the mass of copper(II) oxide (C–A) the mass lost in the expt (B–C) (or from additional columns) Correct subtractions for columns containing plotted data. (ignore any columns which list the number of moles) See appendix 1 (Allow 2 errors) All values must be correct to 2 decimal places 1 1 2 (b) ACE Data D3 D3 D3 Plots any two of mass/moles of copper(II) oxide; mass of basic copper(II) carbonate; mass lost in the experiment with correct labels and units. (If unit error is the same as in 2(a) do not penalise again) (Accept equations as acceptable labels) Suitable scales selected – data to be plotted over more than half of each axis All 10 points plotted and a straight-line passing through the origin and close to the majority of points. 1 1 1 2 (c) ACE Evaluation E1 E2 Identifies the most significant anomalous point and its coordinates from the graph drawn by the candidate not from the table. If points have been plotted correctly the point identified should be for student 3: 2.22 g carbonate / 1.13 g (0.0142 mol) CuO / 1.09 g mass loss, otherwise the most anomalous point is the one furthest from the graph in a perpendicular direction Suggests an appropriate reason for the anomalous point. See Appendix 2 (i) if lower than expected mass of CuO, (higher than expected plotted loss of mass) Solid blown out of tube (by not heating gently) Do not allow this mark for spillage. (ii) if higher than expected mass of CuO, (lower than expected plotted loss of mass) Incomplete decomposition 1 1

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 Question Sections Statement Indicative material Mark 2 (d) ACE Evaluation E2 Mark consequentially – see Appendix 2 If points have been correctly plotted they should indicate (insufficient loss in mass or mass of copper oxide too high) caused by incomplete decomposition 1 2 (e) ACE Conclusions C3 Mark consequentially – see Appendix 2 (this may involve a simple ecf from (d)) (i) For a mass of copper oxide that is too high - refers to heating to constant mass (allow any practical technique which would yield constant mass if carried out e.g. more heat; spreading out the solid; heat for a longer time etc.) (ii) For a mass of copper oxide that is too low - refers to heating more gently 1 2 (f) ACE Data D3 D2 D2 Construction (lines) on graph and values read from the graph (with units) Two of the following expressions used in a calculation: (221 + 18x); 44 + 18(x + 1); 159 (or 2 x 79.5) The value of x correctly evaluated The expected value of x is approximately 0.5 1 1 1 2 (g) ACE Conclusions C1 Refers to one of the following as supporting evidence: straight line, line through origin, few points off the line, Any reference to direct proportionality. If the plotting is so poor that a reverse comment might be appropriate here do not reward 1 2 (h) ACE Conclusions C3 Realises that (i) CO2 gas or CO2 and gaseous H2O could be (collected) and its volume (measured) (not amount) (ii) H2O can be condensed and weighed, (iii) CO2 and/or H2O can be absorbed and weighed 1 2 (i) ACE Evaluation E5 Candidate refers to or calculates a reduction in the % error if using a balance weighing to 3 dp. 1 Qn 2 Total 15

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 Appendix 1 Qn 2 (b) student mass of empty boiling-tube mass of boiling-tube and basic carbonate before heating mass of boiling-tube and residue after heating mass of basic carbonate before heating mass of residue mass of material lost on heating / g / g / g / g / g / g 1 10.32 11.19 10.92 0.87 0.60 0.27 2 10.05 11.56 11.09 1.51 1.04 0.47 3 10.11 12.33 11.24 2.22 1.13 1.09 4 9.94 12.39 11.62 2.45 1.68 0.77 5 9.99 13.73 12.56 3.74 2.57 1.17 6 10.23 14.68 13.28 4.45 3.05 1.40 7 10.01 15.19 13.56 5.18 3.55 1.63 8 9.87 15.80 13.97 5.93 4.10 1.83 9 9.96 16.62 14.66 6.66 4.70 1.96 10 9.84 17.83 15.46 7.99 5.62 2.37

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9701 05 © UCLES 2008 * x * x * x * x * x * x x * x * x * * x * x * x * x * x * x x * x * x * Appendix 2 x represents copper oxide/residue blown out of the tube * represents insufficient decomposition If labelled axes are reversed, points will be on the opposite side of the line drawn. mass of CuO mass of basic carbonate mass of basic carbonate mass of CuO loss in mass loss in mass mass of basic carbonate or mass of CuO mass of basic carbonate or mass of CuO